Current sources which are non-interruptible commonly have two redundant D.C. power sources connected by means of relay or solid state switches to a single receiver. If one of the power supplies fail, the receiver can be carried out by the other power supply. In many applications where redundant power supplies are used, it is desirable to protect the receiver against reversed polarity of the power supply. Moreover, it is also desirable to dynamically switch the receiver from one power supply to the other, and to limit the current variation when the receiver is being connected to the power supply or being disconnected from it.
Typical redundant power supply solutions commonly use a forward biased diode per power supply in one or both of the higher and lower potential lines. These diodes serve to avoid short circuits between power supplies and to protect the receiver from reversed polarity. However, because of the voltage drop across the diode in its forward conducting direction, these diodes reduce the global efficiency of the circuit.
Proposals have been made by others to use relays or solid state switches in redundant power supply applications, and particularly, solutions having metal oxide semiconductor field effect transistor (MOSFET) devices connected to a parasitic or integral diode such that the current is only flowing from power supply to receiver. Willis U.S. Pat. No. 5,598,041, the disclosure of which is incorporated by reference herein, discloses an implementation where the MOSFET device must provide a conduction path through its drain-to-source resistance ‘Ron’ when the power supply polarity is reversed. The MOSFET device provides a conduction path between both power supplies which will damage the power supplies. The device is thus not able to limit the current variation at the receiver power-on, during connection or during disconnection.